Wednesday, August 8, 2007

PS 44-73: Interspecific differences in N mineralization rates and stemflow chemistry among red maple and upland oaks

Heather D. Alexander and Mary A. Arthur. University of Kentucky

In eastern deciduous forests of the U.S., human modification of the historical fire regime has facilitated the spread of red maple (Acer rubrum). This fire-intolerant, but highly adaptable, species is poised to replace ecologically important oaks (Quercus spp.). A relatively unexplored consequence of this apparent species shift is how interspecific differences in canopy and leaf characteristics will affect ecosystem processes like nutrient cycling. Along two ridges in the southern Appalachians of eastern Kentucky, we evaluated seasonal variations in nitrogen (N) mineralization rates in underlying mineral soils of red maple and upland oak (chestnut and scarlet) and tracked stemflow differences following discreet precipitation events. Seasonally, from spring to fall 2006, the two oak species mineralized N at rates faster than or equivalent to red maple, despite previous findings that red maple had lower litter lignin and C:N ratios. Oaks also generated higher carbon inputs via stemflow, especially in fall when oak inputs were ~ 14,000-18,000 mg m-2 C compared to only ~ 7,000 mg m-2 C for red maple. During summer, total N inputs were greatest for red maple (~ 1,600 mg m-2 compared to ~ 700 mg m-2) for the ridges combined. In fall, red maple and chestnut oak had similar total N inputs (~ 2,000 mg m-2), which were slightly greater than inputs from scarlet oak (~ 1,500 mg m-2). This research suggests that red maples do differ from upland oaks in their nutrient cycling via stemflow and N mineralization rates, suggesting potential ecosystem-level consequences of a canopy shift.

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